It has been reported that the cytokine interleukin 17 (IL-17) stimulates epithelial, endothelial, and fibroblastic cells to secrete cytokines such as IL-6, IL-8, and granulocyte-colony-stimulating factor, as well as prostaglandin E2. While expression of IL-17 is restricted to activated T cells, the IL-17 receptor is widely expressed, a property consistent with the pleiotropic activities of IL-17. Moreover, it has been shown that when cultured in the presence of IL-17, fibroblasts could sustain proliferation of CD34+ preferential maturation into neutrophils. As a result, IL-17 could be an early potentiator or even maintainer of T cell-dependent inflammatory reaction and/or an element of the cytokine network that bridges the immune system to hematopoiesis. See, Yao, et al., J. Immunol., 155(12):5483–5486 (1995); Fossiez, et al., J. Exp. Med., 183(6):2593–2603 (1996) Kennedy, et al., J. Interferon Cytokine Res., 16(8):611–617 (1996).
More generally, all novel proteins are of interest. Extracellular proteins play an important role in the formation, differentiation and maintenance of multicellular organisms. The fate of many individual cells, e.g., proliferation, migration, differentiation, or interaction with other cells, is typically governed by information received from other cells and/or the immediate environment. This information is often transmitted by secreted polypeptides (for instance, mitogenic factors, survival factors, cytotoxic factors, differentiation factors, neuropeptides, and hormones) which are, in turn, received and interpreted by diverse cell receptors or membrane-bound proteins. These secreted polypeptides or signaling molecules normally pass through the cellular secretory pathway to reach their site of action in the extracellular environment.
Secreted proteins have various industrial applications, including pharmaceuticals, diagnostics, biosensors and bioreactors. Most protein drugs available at present, such as thrombolytic agents, interferons, interleukins, erythropoietins, colony stimulating factors, and various other cytokines, are secretory proteins. Their receptors, which are membrane proteins, also have potential as therapeutic or diagnostic agents.
Efforts are being undertaken by both industry and academia to identify new, native secreted proteins. Many efforts are focused on the screening of mammalian recombinant DNA libraries to identify the coding sequences for novel secreted proteins. Examples of screening methods and techniques are described in the literature [see, for example, Klein et al., Proc. Natl. Acad. Sci, 93:7108–7113 (1996); U.S. Pat. No. 5,536,637)]. The results of such efforts are presented herein.
Interleukin-17 is a recently described, T cell-derived cytokine, the biological functions of which are only beginning to be understood. Spriggs et al., J. Clin. Immunol. 17: 366 (1997); Broxmeyer, H. E., J. Exp. Med. 183: 2411 (1996). When IL-17 was initially identified as a cDNA clone from a rodent T-cell lymphoma, it was recognized as having a sequence similar to an open reading frame from a primate herpesvirus, Herpervirus saimiri Rouvier et al., J. Immunol. 150: 5445 (1993), Yao et al., Immunity 3: 811 (1995) [Yao-1], Fossiez et al., J. Exp. Med. 183: 2593 (1996). Subsequently, it has been confirmed that this viral protein has many if not all of the immunostimulatory activities found for the host IL-17. Fleckenstein and Desrosiers, “Herpesvirus saimiri and herpesvirus ateles,” In The Herpesviruses, I. B. Roizman, ed, Plenum Publishing Press, New York, p. 253 (1982), Biesinger, B. I. et al., Procl Natl Acad Sci. USA 89: 3116 (1992).
Human IL-17 is a 20–30 kDa, disulfide linked, homodimeric protein with variable glycosylation. Yao-1, supra; Fossier et al., supra. It is encoded by a 155 amino acid open reading frame that includes an N-terminal secretion signal sequence of 19–23 amino acids. The amino acid sequence of IL- 17 is only similar to the Herpesvirus protein described above and does not show significant identity with the sequences of other cytokines or other known proteins. Additionally, the IL-17 encoding mRNA has been detected has only been detected in activated CD4+ memory T cells and PMA/ionomycin stimulated PBMC cells.
Despite its restricted tissue distribution, IL-17 exhibits pleiotropic biological activities on various types of cells, such as fibroblasts, endothelial cells and epithelial cells. Spriggs, M. K., supra.; Broxmeyer, H. E., supra. IL-17 has been found to stimulate the production of many cytokines: TNF-α and IL-1β from macrophages [Jovanovic et al., J. Immunol 160: 3513 (1998)]; IL-6, IL-8 and the intracellular adhesion molecule (ICAM-1) from human fibroblasts. Fossiez et al., supra, Yao et al., J. Immunol 155: 5483 (1995) [Yao-2]; granulocyte-colony-stimulating factor (G-CSM) and prostaglandin (PGE-2) form synoviocytes, Fossiez et al., supra. Through the induction of a number of cytokines, IL-17 is able to mediate a wide-range of response, mostly proinflammatory and hematopoietic. This has led to the suggestion that IL-17 may play a pivotal role in initiating or sustaining an inflammatory response. Jovanovic et al., supra.
Consistent with IL-1 7's wide-range of effects, the cell surface receptor for IL-17 has been found to be widely expressed in many tissues and cell types Yao et al., Cytokine 9: 794 (1997) [Yao-3]. While the amino acid sequence of the hIL-17 receptor (866 a.a.) predicts a protein with a single transmembrane domain and a long, 525 amino acid intracellular domain, the receptor sequence is unique and is not similar to that of any of the receptor from the cytokine/growth factor receptor family. This coupled with the lack of similarity of IL-17 itself to other known proteins indicates that IL-17 and its receptor may be part of a novel family of signaling proteins and receptors.
IL-17 has further been shown, by intracellular signaling, to stimulate transient Ca2+ influx and a reduction in [cAMP]i in human macrophages. Jovanovic et al., supra. Fibroblasts and macrophages treated with IL-17 induce the activation of NF-κB, Yao-1, supra, Jovanovic et al., supra., while macrophages treated with it activate NF-κB and mitogen-activated protein kinases. Shalom-Barek et al., J. Biol. Chem. 273: 27467 (1998).
The present invention describes the cloning and characterization of two novel proteins, termed PRO1031 (IL-17B) and PRO1122 (IL-17C), and active variants thereof, that are similar in amino acid sequence to IL-17.